1. Field of Invention
The present invention relates generally to a processing system and method for polishing a substrate, and specifically, to an apparatus and method for loading the processing system.
2. Background of Invention
In semiconductor wafer processing, the use of chemical mechanical planarization, or CMP, has gained favor due to the enhanced ability to increase device density on a semiconductor workpiece, or substrate, such as a wafer. As the demand for planarization of layers formed on wafers in semiconductor fabrication increases, the requirement for greater system (i.e., process tool) throughput with less wafer damage and enhanced wafer planarization has also increased.
Two exemplary CMP systems that address these issues are described in U.S. Pat. No. 5,804,507, issued Sep. 8, 1998 to Perlov et al. and in U.S. Pat. No. 5,738,574, issued Apr. 15, 1998 to Tolles et al, both of which are hereby incorporated by reference. Perlov et al. and Tolles et al. disclose a CMP system having a planarization system that is supplied wafers from cassettes located in an adjacent liquid filled bath. A transfer mechanism, or robot, facilitates the transfer of the wafers from the bath to a transfer station. The transfer station generally contains a load cup that positions wafers into one of four processing heads mounted to a carousel. The carousel moves each processing head sequentially over the load cup to receive a wafer. As the processing heads are loaded, the carousel moves the processing heads and wafers through the planarization stations for polishing. The wafers are planarized by moving the wafer relative to a polishing pad in the presence of a slurry or other polishing fluid medium. The polishing pad may include an abrasive surface. The slurry typically contains both chemicals and abrasives that aid in the removal of material from the wafer. After completion of the planarization process, the wafer is returned back through the transfer station to the proper cassette located in the bath.
Generally, the wafer cassettes remain in the bath during operation of the system. As the wafers are polished, the system eventually requires that the cassettes containing polished wafers be removed from the bath to create space for new cassettes containing unpolished wafers. During the process of loading the bath, the system is shut down to prevent accidental interaction between operators exchanging cassettes in the bath and robotic equipment used to retrieve wafers from the bath. During this period, no wafers are processed resulting in the loss of valuable production time and factory capacity (i.e., adversely affecting substrate throughput).
Therefore, there is a need in the art for an apparatus that loads substrates in a chemical mechanical polishing system having minimal impact on substrate throughput.
One aspect of the present invention generally provides an apparatus for loading a semiconductor processing system. In one embodiment, a loader includes a wall having an exterior side with one or more apertures formed therethrough. A door assembly is movably coupled to the wall in each of the apertures and is adapted to temporarily retain substrates. A first portion of the door assembly substantially closes the aperture when the door assembly is in a first or closed position, and a second portion of the door assembly substantially closes the aperture when the door assembly is in a second or open position.
In another embodiment of the invention, a loader may further include a wafer mapper, an interlock, a wafer sensor and a wetting system. The loader may additionally be coupled to a factory interface and one or more polishing modules having a robot positioned therebetween. The robot transfers the wafers between the one or more polishing modules and the substrate storage cassette.
In yet another embodiment, the invention provides a robot for transferring a substrate in a processing system. The robot includes a central body having a shaft rotationally extending therefrom. An arm coupled at a proximate end to the shaft by a rotary actuator. A gripper is coupled to a distal end of the arm.
In another aspect of the invention, a method for loading a semiconductor processing system is provided. In one embodiment, a method for loading a processing system includes providing a first substrate cassette supported by a door assembly in a position where substrates contained in the first substrate cassette may be accessed by a robot that transfers the substrates to a processing area for processing; moving the door assembly supporting the first substrate cassette to a position where the first substrate cassette may not be accessed by the robot; replacing the first substrate cassette with a second substrate cassette while the system continues to process other substrates; and returning the door assembly to the position where the second substrate cassette may be accessed by the robot.
In another embodiment, the method includes providing a first substrate cassette having one or more substrates, securing the substrate with a gripper disposed at a distal end of an arm of a robot, removing the substrate from the cassette by a combined lateral movement of the robot and rotational movement of the arm about the center of the robot that produces a movement of the substrate substantially perpendicular to the lateral movement of the robot.